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Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , Weijiang Yang , "Kirill A . Shutemov" , John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com, akpm@linux-foundation.org, Andrew.Cooper3@citrix.com, christina.schimpe@intel.com, david@redhat.com, debug@rivosinc.com, szabolcs.nagy@arm.com, torvalds@linux-foundation.org, Yu-cheng Yu , Pengfei Xu References: <20230613001108.3040476-1-rick.p.edgecombe@intel.com> <20230613001108.3040476-29-rick.p.edgecombe@intel.com> <76a87cdf-4d4f-4b3f-b01f-0540eab71ac7@sirena.org.uk> From: Dave Hansen In-Reply-To: <76a87cdf-4d4f-4b3f-b01f-0540eab71ac7@sirena.org.uk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: hqm3duec7e73df7bh6jtd5q3jg4bsp84 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: ED2A712000A X-Rspam-User: X-HE-Tag: 1687909563-964652 X-HE-Meta: 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 e6meBhqX /xG9ENwgfw/H4aGsWEUZD/7UL/V6mNQyS0MYsk1lcCWUQNK/vrXQS35dXxbaRyhdMil9XJQcRLHso9oLW46rixv9XP+40lIdZEjo/ort5A302g/Ny+gVOfahkVtRavk65E8wXzu0oXZ9xWs+/e+BfiQ4khl9uo9NbfW/FDxXQudeaIROePPCxSuHvuoUD7nkWw+6X3Zv+k6LWRu723vrX+fDPYg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/27/23 10:20, Mark Brown wrote: > On Mon, Jun 12, 2023 at 05:10:54PM -0700, Rick Edgecombe wrote: > >> +static void unmap_shadow_stack(u64 base, u64 size) >> +{ >> + while (1) { >> + int r; >> + >> + r = vm_munmap(base, size); >> + >> + /* >> + * vm_munmap() returns -EINTR when mmap_lock is held by >> + * something else, and that lock should not be held for a >> + * long time. Retry it for the case. >> + */ >> + if (r == -EINTR) { >> + cond_resched(); >> + continue; >> + } > This looks generic, not even shadow stack specific - was there any > discussion of making it a vm_munmap_retry() (that's not a great name...) > or similar? I didn't see any in old versions of the thread but I > might've missed something. Yeah, that looks odd. Also odd is that none of the other users of vm_munmap() bother to check the return value (except for one passthrough in the nommu code). I don't think the EINTR happens during contention, though. It's really there to be able break out in the face of SIGKILL. I think that's why nobody handles it: the task is dying anyway and nobody cares. Rick, was this hunk here for a specific reason or were you just trying to be diligent in handling errors?